High resolution geodesy for active, deforming volcanoes

一些火山喷发造成了巨大的经济和人道主义代价，但有助于预测它们的措施可以减少它们的影响。岩浆到达地表的路径是不可能直接观测的，我们必须依靠小地震、瓦斯涌出和地表形变等次生迹象来推断岩浆运动，我们建议的工作使用后者。具体地说，我们将使用被称为InSAR的卫星雷达干涉测量技术来探测地球表面位置不足1厘米的变化。InSAR可以测量岩浆储集层的压力，这种压力通常会使地表变形数十公里，并持续数年。然而，越来越清楚的是，火山上还有其他规模较小、发生得更快的信号，目前的InSAR不太适合这些信号。我们计划使用TerraSAR-X卫星观测这些信号，该卫星的工作波长比它的前身更短，每11天产生2米分辨率的图像。我们选择以拉丁美洲一系列活跃喷发的火山为目标，这些火山靠近主要人口中心和基础设施，尤其令人关切。雷达测量在这一地区尤其重要，因为频繁的云层覆盖会使直接和空中观测变得困难。我们将讨论与火山穹顶的增长、火山侧翼的主要不稳定性以及伴随着爆发的危机而来的地表变形模式有关的科学问题。一些火山几乎不间断地喷发，但每一两年就会发生一次特别危险的喷发危机。在这些火山，我们将使用频繁的TerraSAR-X图像来了解是否发生了隆起和下沉：1)在大喷发前持续几个月的地震和爆炸的高峰期；2)在喷发本身期间迅速；或3)随着火山在喷发后放松进入静默期，速度较慢。其他火山正在从缓慢移动的粘性岩浆中形成新的熔岩穹顶。当新材料添加得特别快时，穹顶非常不稳定，坍塌伴随着危险的水流和灰柱。高分辨率雷达图像中的细微特征将为我们提供有关穹顶状态、增长速度和坍塌事件的线索。最后，低分辨率的图像显示，随着新的熔岩流和火山灰的堆积，哥斯达黎加火山Arenal的侧翼正在迅速向山下滑动--突然的崩塌可能会导致大规模的滑坡，甚至可能引发一次重大的爆炸性喷发。新的、更高分辨率的图像将告诉我们，火山侧翼是作为一个单一的连贯块移动，还是实际上被分成几个以不同速度移动的较小块。我们将与负责监测这些火山的火山观测站密切合作，以最大限度地发挥我们工作的实际效用。

Some volcanic eruptions have enormous economic and humanitarian costs, but measurements that help anticipate them can reduce their impact. The pathway of the magma to the surface is impossible to observe directly and we must rely on secondary signs such as small earthquakes, gas emission and surface deformation to infer magma movement Our proposed work uses the latter. Specifically, we will use the satellite radar interferometry technique known as InSAR to detect changes of less than 1 cm in the position of the earth's surface. InSAR can measure the pressurisation of magma reservoirs, which typically deforms the ground surface over distances of tens of kilometres and lasts for several years. Yet, it is becoming increasingly clear that there are other signals on volcanoes that are smaller in scale and occur more rapidly for which the current use of InSAR is poorly suited. We plan to observe these signals using the satellite TerraSAR-X, which operates at a shorter wavelength than its predecessors, producing images with 2 m resolution every 11 days. We have chosen to target a range of actively erupting volcanoes in Latin America, whose proximity to major population centres and infrastructure are a particular cause for concern. Radar measurements are especially important in this region since frequent cloud cover can make direct and airborne observations difficult. We will address scientific questions related to the growth of volcanic domes, major instabilities on the flank of the volcanoes and the patterns of surface deformation that accompany eruptive crises. Some volcanoes erupt almost continuously, but with especially dangerous eruptive crises occurring every year or two. At these volcanoes, we will use the frequent TerraSAR-X imagery to learn whether uplift and subsidence occur 1) during the heightened period of earthquakes and explosion lasting several months before a major eruption; 2) rapidly during the eruption itself or 3) more slowly as the volcano relaxes into a quiet period following the eruption. Other volcanoes are forming new lava domes from slow-moving, viscous magma. When new material is added particularly quickly, the dome is very unstable and collapses are accompanied by dangerous flows and ash columns. Subtle features in the high resolution radar images will give us clues as to the state of the dome, its growth rate and collapse events. Finally, low resolution images have shown that the flank of Volcan Arenal in Costa Rica is sliding rapidly downhill as new lava flows and ash falls accumulate - a sudden failure could cause a massive landslide and possibly even trigger a major explosive eruption. The new, higher resolution images will tell us if the volcano flank is moving as a single coherent block, or is actually broken up into a number of smaller blocks moving at different rates. We will work closely with the volcano observatories responsible for monitoring these volcanoes to maximize the practical utility of our work.